1. Field of the Invention
The present invention relates to a technique of removing shavings which are generated at the time of a so-called scratch processing for removing unnecessary portions of a sample by scraping the sample using a probe of a scanning probe microscope, and more particularly relates to a remaining shavings removing technique which is effective in the black defect repair, etc. of a photo mask.
2. Description of Related Art
As the defects of a photo mask used for fabricating semiconductor devices, there are a defect (a so-called black defect) which distorts a translucent pattern due to an excessive attachment, a defect which forms an excessive phase shifter pattern during the fabrication of a phase shifter pattern, and a defect (a so-called white defect) which distorts a translucent pattern due to a defect in a light shielding film pattern. These defects are generally named as the mask defects. The photo mask is carefully subjected to the repairing processing of the defects thereof and then used for the semiconductor device fabricating process. This is because, since many semiconductor devices are fabricated based on the mask, the defects of the photo mask itself are reflected on all the semiconductor devices to be fabricated. There are some mask repairing methods for removing residual defects such as the black defect or the excessive phase shifter pattern. The first method is arranged in a manner that a laser beam is focused and irradiated on defects to evaporate and remove the defects. This method causes a problem that, as a result of the heat of the laser irradiation, distortion appears at the processed edge portion of the mask and so the configuration of the mask after the processing is not so good. Further, there arises such a problem that since the narrowing of the laser beam is limited, the micro-fabrication of 500 nm or less is difficult. The second method is arranged in a manner that a converged ion beam is irradiated on a photo mask to remove and repair the defects thereof through the spattering. According to this method, it is known that gallium as an ion source is implanted into a quartz as a mask substrate in the ion beam irradiation area to generate gallium stains and so light transmittance is degraded, and that ions are also irradiated on the quartz substrate at the peripheral portions of the residual defects and so the transmissivity of the substrate is degraded due to the excessive spattering. Thus, the mask itself is damaged due to the repairing process. These matters increasingly have become large problems in accordance with the recent tendency of the micro-fabrication of the semiconductor pattern.
Recently, as a method of such a kind of the mask repairing, there has been developed and notified a technique in which excessive portions such as black defects are scraped away by the probe of a probe microscope such as an atomic force microscope (AFM). The invention disclosed in a patent document 1 intends to provide a defect repairing method of the photo mask in which there is no damage to a quartz substrate and portions other than defects after the repair of the residual defects formed on a mask, then residual defects of 500 nm or less can be removed effectively, and the end point of the repair can be detected easily and a scanning probe microscope used therefor. To this end, as shown in FIG. 7A, a mask is set to the scanning probe microscope, and the stage of the microscope is moved so that the probe D is positioned just above the residual defect A. Next, as shown in FIG. 7B, the tip end of the probe D is approached to a position where it contacts the residual defect A. Then, as shown in FIG. 7C, while scanning the probe in the X and Y directions only in the region of the residual defect A, the probe D is pushed down to apply a load to the defect thereby to scratch the defect to scrape the defect away. Next, as shown in FIG. 7D, when the tip end of the probe D reaches the quartz substrate B, the push-down operation and the scanning operation in the X and Y directions of the probe D are stopped. Next, as shown in FIG. 7E, the probe D is largely separated from the mask pattern. Finally, as shown in FIG. 7F, cleaning air is blown toward the mask from a clean air gun E to completely remove the shavings form the mask, whereby the defect repairing method of the photo mask is completed.
Although this method scrapes the defect portions off by using the probe, since this probe is one for the probe microscope, there does not arise the defects caused in the case of using a laser beam or an ion beam. Further, since the defect area is suitably scanned in the X and Y directions during the defect repairing operation for scraping the defect portions off, the repairing state can be observed. Furthermore, since the scraping operation can be performed while observing the processing state, there does not cause such a problem that there remains a portion to be scraped or there is a portion too scraped. However, according to this method, as shown in FIG. 6, shavings remain around the scraped portion and so also remain on the surface of the sample having been processed (hereinafter, the shavings are called as remaining shavings). According to the aforesaid method, the cleaning air is blown toward the mask from the clean air gun to remove the remaining shavings from the mask. However, in such an on-machine remaining shavings removing processing using the air gun, there arises a case that particles of nano-order sizes are scattered within the apparatus to pollute the mask as shown in FIG. 5. In particular, the residual shavings collect at the surface of the mask, due to the surface tension of adsorbed water existing on the mask surface and/or electrostatic charges caused by friction, can not be removed easily.
[Patent Document 1] JP-A-2003-43669 (“Method of Correcting Defect of Photomask and Scanning probe microscope”, paragraphs [0016], [0016], FIG. 1)